Question: Are shoppers more or less likely to use credit cards for "impulse purchases" that they decide to make on the spot, as opposed to purchases that they had in mind when they went to the store? Stop every third person leaving a department store with a purchase. (This is in effect a random sample of people who buy at that store.) A few questions allow us to classify the purchase as impulse or not. Here are the data on how the customer paid:

Credit Card?
Yes No
Impulse purchases 13 18
Planned purchases 35 31

Estimate with 95% confidence the percent of all customers at this store who use a credit card. Give numerical summaries to describe the difference in credit card use between impulse and planned purchases. Is this difference statistically significant?